Congenital Hearing Loss [Permanent Childhood Hearing Loss]
This is defined as an hearing loss that is present at birth. Perhaps a more useful term is Permanent Childhood Hearing Impairment or Loss, which includes congenital hearing loss as well as conditions that cause permanent hearing impairment in early childhood. These terms are often used interchangeably.
Hearing loss can be either conductive or sensorineural in nature. In childhood the commonest cause is related to middle ear fluid. This discussion deals with the much rarer sensorineural hearing loss.
According to the American Academy of Paediatrics significant permanent bilateral hearing loss occurs in 1%-3% of every 1,000 live births4. Significant hearing loss is defined as being greater than 40dB in the better ear. This almost doubles up to the age of 9 years.
- · More than 50% of prelingual deafness in developed countries is attributable to genetic factors.
- · 25% are due to environmental causes of HL: which may include adverse perinatal factors, for example, extreme prematurity, hyperbilirubinaemia, aminoglycoside drugs, hypoxia, meningitis and congenital infections and head trauma
- · 25%: no cause is found for the hearing loss
- · Seventy percent of prelingual hereditary HL is nonsyndromic (NSHL), the remaining
- · 30% is syndromic (characterized by accompanying symptoms).
- · Approximately 80% of genetically caused prelingual NSHL has an autosomal recessive mode of inheritance, while autosomal dominant cases account for approximatel 15%, and X-linked cases for 2 to 3%
The evaluation of a child with permanent hearing loss requires a careful history, thorough examination and often extensive investigations. A multi-disciplinary team is responsible for this evaluation as well as for the institution of treatment and hearing rehabilitation. The advent of newborn screening has been responsible for the early identification of a high proportion of PCHI. In NSW an automated ABR (auditory brainstem response) is used for this screening, and is called the SWISH program (The StateWide Infant Screening – Hearing). The goal is to identify all babies born in NSW with significant permanent hearing loss. Significant hearing loss is defined as being greater than 40dB in the better ear.
4.2%-9.5% of children fail the initial SWISH test, and are required to undergo a second screening test. Overall about 4% of children require formal audiologic assessment with the following results found.
ox 1 Why it is important to investigate deafness?
This table outlines the results from the SWISH program from 2006-2010. [from the NSW Department of Health Evaluation of the SWISH Program 2011]
Principles in the Evaluation of Permanent Childhood Hearing Loss
Documenting and measuring the type and degree of hearing loss
1. Degree of hearing impairment: mild, moderate, severe, profound (mild hearing
loss 20–40 dB HL, moderate hearing loss 41–70 dB HL, severe hearing loss
71–95 dB HL, profound hearing loss >95 dB HL, using the average of the
pure tone threshold hearing levels at 250, 500, 1000, 2000, 3000, 4000 Hz
in the better ear)
2. Bilateral or unilateral sensorineural hearing loss
3. Bilateral or unilateral fi xed conductive hearing loss
4. Bilateral or unilateral mixed hearing loss
5. With or without vestibular function
6. Auditory neuropathy spectrum disorder
Important Information on History
1. Maternal health in pregnancy, especially a history of febrile illness with rash, herpes
infection, gestational or permanent diabetes, maternal intake of alcohol and ototoxic
drugs, rhesus status, syphilis status, rubella status, evidence of intrauterine growth retardation and/or microcephaly
2. Perinatal history: perinatal asphyxia, prematurity, neonatal jaundice, apnoea, acidosis, meningitis, persistent fetal circulation, ototoxic medication, intracranial haemorrhage
3. Acquired infection: meningitis or other infections
4. Child’s developmental milestones, including age at smiling, sitting, walking, and communication
and language skills. Delay may be global and suggest syndromic diagnoses, or motor which may suggest vestibular involvement
5. Features to suggest autoimmune disease such as sudden or progressive deafness, with evidence of multisystem disease, for example, eye or joint symptoms
6. Head injury with loss of consciousness and/ or associated audiovestibular symptoms
7. Features to suggest metabolic conditions such as developmental delay, coarse appearance, skeletal problems
8. Features to suggest cardiac arrhythmia, for example, funny turns, faints, fits, breath holding
9. Ototoxic drugs: exposure to aminoglycosides, platinum derivatives, loop diuretics, quinine derivatives, salicylates
10. Features to suggest mitochondrial diseases, for example, maternal family history of hearing loss, exposure to aminoglycosides, diabetes, stroke-like episodes, encephalopathic episodes or multisystem involvement.
The family history should be investigated for:
2. Deafness, to include a three-generation family tree with documentation of type of deafness, age of onset, features of progressive hearing loss with or without vestibular symptoms/ failure
3. Developmental delay, especially motor delay, or multisensory handicap or learning difficulties
4. Metabolic disease
5. Heart disease, arrhythmias or sudden death
6. Syndromic features such as renal disease or failure, thyroid disease, operations on neck cysts or sinuses
7. Pigmentary abnormalities such as skin, hair or eye hypo- or hyperpigmentation, café au lait spots
8. Eye disease such as cataracts or visual loss
9. Cleft palate.
Particular features in the history to be checked in
the clinical examination include:
1. Height, weight and head circumference
2. Face to check for dysmorphic features, microsomia, hypoplasia, asymmetry
3. Ears to check shape, preauricular pits or sinuses, tags
4. Neck to check for goitre, sinuses, pits, short, webbing
5. Hands to check for extra digits, missing digits, appearance of digits, abnormal thumbs
6. Eyes to check iris pigmentation, coloboma, dystopia canthorum, hypertelorism
7. Skin to check for hypo- or hyperpigmentation
8. Spine to check for scoliosis, asymmetry
9. Cardiovascular to check for heart murmurs
10. General neurological examination
11. Assessment of the child’s vestibular function
12. Parental features – dysmorphism, skin abnormalities.
1. Clinical history
2. Clinical examination
3. Family and sibling audiograms
4. Congenital rubella , toxoplasmosis, syphilis, HSV, Cytomegalovirus (CMV) testing
5. Genetic testing
8. ECG – in certain groups
10. Vestibular assessment: Approximately 30–40% of children with bilateral severe to profound deafness have bilateral vestibular dysfunction
MRI is the imaging of choice for detection of mild cochlear dysplasias as well as cochlear nerve hypoplasia, the presence of labyrinthitis obliterans after meningitis and neural tumours. CT imaging is more suitable for investigation of bony, outer and middle ear.
The most common abnormalities seen on MRI are cochlear dysplasia (30%), cochlear nerve abnormalities
(18%), enlargement of the endolymphatic duct in 10% and enlargement of the endolymphatic sac in 7%.
Children with unilateral SNHL have a higher incidence of abnormality on MRI at 62% compared to 38% in children with bilateral SNHL.
Genetic Causes of Permanent Childhood Hearing Loss
- To date, almost 150 loci for non-syndromic deafness alone have been mapped (assigned a chromosomal location),
- 57 for dominant deafness. Nomenclature is DFNA. This is usually post-lingual to adult onset and is progressive.
- 77 for recessive deafness. Nomenclature is DFNB. This is usually pre-lingual or congenital is moderate to profound in severity across all frequencies.
- 8 for X-linked deafness, and more than 40 genes identified.
Current genetic testing is limited to the most common genes or those in which there are phenotypic clues. The (eg, GJB2, SLC26A4 in cases with enlarged vestibular aqueducts, m.1555A>G where there has been aminoglycoside exposure or progressive hearing loss, X-linked deafness DFN3 in which there is pathognomonic inner ear radiology)
Although autosomal recessive SNHL is heterogeneous, mutations in the connexin 26 ( GJB2) gene at the DFNB1 locus contribute about half of all hereditary cases in Australia and the United States. Mutations of GJB2 at exon 1 and 2, and analysis for deletion at GJB6 are the commonest testing done here.
More than 400 syndromic forms of deafness have been described, although only the most common
- Waardenburg syndrome types 1 and 2,
- Treacher Collins syndrome,
- Branchio-oto-renal (BOR) syndrome
- Usher syndrome.
A heterogeneous group of children present with impaired speech perception and have difficulty with processing rapidly changing acoustic signals. The audiometric descriptors may range from mild to severe to profound hearing loss patterns. It has recently been suggested that this group should be described as having an auditory neuropathy spectrum disorder (ANSD). The true prevalence of ANSD is unknown and it is estimated that about 10% of all infants with hearing disorders show symptoms of ANSD.